1. Field of the Invention
The present invention relates to recordable optical memories such as optical disk drives and more particularly to optimizing the signals involved in writing to the optical memory.
2. Description of the Related Art
Optical disk drives capable of writing data to an optical disk use a laser diode driver to generate the signals used to drive and modulate the laser diode typically used to write to the optical disk. This is in part due to the fact that laser diodes require relatively high current and specially conditioned signals to operate without damaging the laser diode. In many disk systems, the laser diode and the laser diode driver are mounted together on the optical head of the disk drive, so that the entire assembly is movable with respect to the surface of the optical disk. This arrangement simplifies the optics of the system, allowing fixed optics to be used for focusing light on the disk and collecting light from the disk. To limit the weight, and thus the inertial lag of the optical head, convention optical disk drives limit the electronics mounted on the optical head to those needed for performance. It is consequently conventional to provide a controller remote from the optical head and the laser diode driver that performs processing and generates the signals supplied to the circuitry of the laser diode driver.
In the typical case the optical disk drive controller is one integrated circuit or chip mounted at some distance from the laser diode driver circuitry, which is provided on a second chip. The optical disk drive controller is mounted on a printed circuit board, with other drive electronics, with the printed circuit board rigidly mounted with respect to the frame of the optical disk drive. The laser diode driver is also a chip and typically is mounted on a small printed circuit board with the laser diode on the optical head. A flexible cable connects the controller's printed circuit board to the driver's printed circuit board. This flexible cable carries the signals from the controller that determine how and with what signals the laser diode driver drives the laser diode.
There are some instances when feedback is provided from the laser diode to the optical disk controller. For example, the operating characteristics of laser diodes such as gain and wavelength are sensitive to variations in the temperature of the laser diode around its nominal operating temperature. Some optical disk drives measure the laser diode temperature and provide a measure of the temperature to the optical disk controller, which adjusts the drive signal to accommodate the changed operating characteristics associated with that temperature.
Other optical disk drives may monitor the output power of a laser diode, for example by sampling the output of the laser diode using a monitor diode. The optical disk drive adjusts the drive current to the laser diode to adjust the output level of the laser diode or to accommodate different storage media. Such optical disk drives are not, however, capable of detecting timing variations that might produce write errors.